The present invention relates to a jet engine, especially for an aircraft, with at least one hollow shaft and/or low pressure shaft that is rotatably supported in at least one bearing about a center axis, on which shaft at least respectively one high and/or low pressure compressor as well as at least respectively one high and/or low pressure turbine is arranged, whereby the jet engine furthermore comprises an electromechanical unit in order to provide at least a motor function for starting the jet engine and/or a generator function for supplying power, whereby the electromechanical unit is centrally arranged about the center axis and whereby the electromechanical unit is further embodied as an active magnetic bearing, which supports or bears the hollow shaft and/or low pressure shaft.
Such jet engines are sufficiently known, whereby the means for starting the jet engine as well as the means for generating the electric power are arranged separate from one another on the jet engine. For being brought into operation, the jet engine must be mechanically started, whereby in a two-shaft-engine the shaft of the high pressure compressor is set into rotation via a mechanical engagement or interaction. Furthermore, jet engines comprise means for generating an electric power, which can be arranged in the form of a generator in or on the engine. In that regard, the electric power is needed for the operation of various electrical devices of the aircraft, whereby present developments show that the required electric power of the aircraft is further increasing due to a growing electrification of various different systems or devices. The jet engine considered according to the present invention especially relates to a fan engine, which is embodied as a two-shaft-engine and the fan represents a low pressure compressor which pre-compresses the air flowing into the engine and also generates a bypass shroud flow around the centrally ejected or discharged hot exhaust gas jet.
From the US 2002/0122723 A1, a jet engine of the above general type is known, which comprises a generator that is integrated in the high pressure compressor of the jet engine. The engine comprises compressor blades that are shrouded, whereby an electric generator is arranged outside of the shroud. This consists of a stator that encompasses an electric coil, as well as a rotor that is connected with the engine shaft in such a manner that this carries out a rotational motion in the same manner. The rotor arrangement carries out a rotational motion within the stator, and induces an electric voltage in the coil of the stator. The rotor elements are arranged on the outside on the blade elements of the high pressure compressor and extend radially outwardly into the stator of the generator.
The bearing support of the hollow shaft, on which the high pressure compressor is rotatably arranged, as well as the bearing support of the low pressure shaft, on which the low pressure compressor is arranged, are supported via mechanical bearings, such as roller bearings for example. Additionally, the at least one shaft of the jet engine can be rotatably supported via active magnetic bearings, whereby the active magnetic bearing arrangement according to the prior state of the art merely represents a respective partial bearing support of the shafts. For providing a lubrication system for the mechanical bearing arrangement, especially a so-called gearbox is necessary, which is arranged within the engine pod on the outside of the jet engine and is driven via a shaft arrangement, the so-called power shaft, by means of a power takeoff from at least the low pressure shaft and/or the hollow shaft.
Such a combined bearing support between mechanical and active magnetic bearing support is disclosed in the U.S. Pat. No. 6,378,293 B1. Therein a jet engine comprises a plurality of shafts, which respectively connect the compressor sides with the turbine sides of the jet engine. In the hot part of the jet engine, these shafts are supported by electromagnetic bearing arrangements, whereby mechanical bearing arrangements support the remaining part of the turbine. In that regard, while the arrangement offers a partial bearing support by means of electromagnetic bearings, yet nonetheless a lubrication system is further necessary due to the remaining mechanical bearing arrangements. The generator for generating the electric power, which is necessary in order to supply the electromagnetic bearing arrangements, is therein arranged at the end side far from the respective electromagnetic bearing arrangements, and is embodied as a separate unit. A portion of the electric power provided by the generator is supplied to the aircraft via an output, whereby the portion of the electric power that is needed for supplying the electromagnetic bearing arrangements is supplied to the electromagnetic bearing arrangements via a control unit by means of separate electric lines.
In the known systems although they comprise a generator, electromagnetic bearing arrangements as well as corresponding power electronics for the control and respective connection of the system, the problem arises that a lubrication system is further necessary due to the remaining mechanical bearing support, which lubrication system must especially be made available through an outside arranged gearbox. Furthermore a high space demand is required, because both the respective electromagnetic bearing arrangements as well as the generator arrangement are accommodated separate from one another in the jet engine. Due to the high costs arising thereby as well as the high weight and the expanded space demand, the use of an active magnetic bearing is realizable only with limitations or is not sensibly economically realizable. With respect to the known generator arrangement within the jet engine, the problem further arises that the generator only serves for power generation, but is not suitable as an electric motor for starting the jet engine, whereby the starting function must further be realized via the gearbox arranged outside on the jet engine. The gearbox can encompass both a starter function as well as also a generator function, whereby this requires a considerable space demand on the circumference of the jet engine, represents a high weight, and comprises a high maintenance requirement. A further disadvantage exists in that the gearbox encompasses means embodied for starting the jet engine, which must be carried along as an unusable device during the flight operation and thus brings about a “dead weight”.
In this regard, the U.S. Pat. No. 5,867,979 attempts to provide a remedy that proposes several motor/generator units, which also can be combined with an electromagnetic shaft bearing.
However, in connection with the use of combined motor/generator/bearing units, further technical problems result, which arise especially in maneuvers with high g loads or shock loads. Hereby the air gap in the electromagnetic bearing can become so small that the so-called “Barkhausen Effect” occurs. According to the Barkhausen Effect, the magnetization of ferromagnetic materials takes place in many small jumps or steps. The approach of a magnetic pole to an iron piece about which a coil is placed increases the magnetic induction in the iron piece due to flipping or reversal of the individual ferromagnetic domains and respectively produces a momentary induction current in the coil.
In the case of the magnetic bearing, this leads to the result that the mutual opposite repulsion forces, on which this bearing principle is based, collapse and produce a force in the opposite direction, that is to say attraction forces.
This is not acceptable especially in aircraft. It is therefore the object of the present invention to provide a jet engine in which means for the bearing support of the at least one engine shaft as well as means for the power supply of the active magnetic bearing arrangement and of the aircraft as well as means for the starting of the jet engine are embodied in an integrated unit in a space and weight saving manner. Thereby, the disadvantages of the prior state of the art are to be avoided and the high safety requirements necessary for the operation of aircraft are to be satisfied.